The present embodiments relate to generating an at least three-dimensional display data set of a time parameter relating to chronological spreading of a contrast medium introduced into a vessel system.
It is known in the field of angiography to administer contrast medium that may be clearly recognized in image recordings (e.g., x-ray recordings) and thus permits an assessment of the blood flow and the blood perfusion in the vascular system of a patient and also in the tissue. A classic technique for following the spread of the contrast medium is digital subtraction angiography. In this process, a mask image without contrast medium is recorded. After this, raw images are recorded, often as a chronological series in a time range in which the contrast medium passes through the target region or vascular system of interest, and in which the contrast medium may be seen. In order to remove anatomy that causes interference during evaluation, x-ray images of the digital subtraction angiography are generated in that the mask image is subtracted from the raw image so that essentially only image information relating to the contrast medium remains. In order to obtain better orientation, the two-dimensional digital subtraction angiography may be operated from a plurality of projection directions simultaneously (e.g., by using a biplane system). There may then exist raw images and mask images of the target region, for example, from mutually perpendicular projection directions, so that x-ray images for these mutually perpendicular projection directions are obtained and may be observed and evaluated for diagnosis.
A plurality of time parameters may be determined from two-dimensional subtraction angiography x-ray images, which show the behavior of the contrast medium or are derived therefrom if the time-intensity curves (TIC) are observed in the x-ray images. Herein, for at least some of the image points of interest, the image data (e.g., the intensity) of the x-ray image for all the time points of the series for which an x-ray image exists are plotted against the recording times so that a time-intensity curve is produced (e.g., a contrast medium curve). This is accessible to classic methods of evaluation, and thus, for example, the time to maximum of the contrast medium concentration may be observed at the image point, this usually being known as “time to peak” (TTP). A further, often used time parameter is the mean transit time (MTT), which may be defined in a variety of ways (e.g., relative to the maximum value of the time-intensity curve). The time-intensity curve is also known as TIC.
Importance is also placed on contrast medium-supported examinations in relation to the human brain (e.g., as far as blood perfusion of the parenchyma is concerned). In order to conduct examinations in this regard, regions of interest (ROI) may be defined in the subtraction angiography x-ray images, which are, as far as possible, not overlaid by relatively large vessels. Integration over the time-intensity curve provides information on the quantity of contrast medium that has flowed through at an image point. If the time-intensity curve is observed for a highly interesting region, then this applies for all structures through which x-rays pass. From this, the cerebral blood volume (CBV) and the cerebral blood flow (CBF) may be derived (e.g., in relation to a reference region).
In the prior art, aids that are intended to assist a user in the evaluation of two-dimensional subtraction angiography x-ray images (e.g., for imaging with a biplane x-ray apparatus) have become known. In this regard, time-intensity parameters may be determined from the time-intensity curves for each of the individual x-ray images and, for example, color-coded or displayed using a gray-value scale. Already known, for example, are color-coding systems in which early TTP is assigned a red color, medium TTP is assigned a green color, and high TTP is assigned a blue color. By observing the plurality of projection directions (e.g., two projection directions), the user is able to draw conclusions about where in three-dimensional space interesting vessels/tissues may be found. If it is desired to obtain actual three-dimensional or even four-dimensional information, in place of two-dimensional raw images and assigned mask images, three-dimensional image data sets may be recorded. For example, a rotation of a C-arm about the target region takes place, and reconstruction of three-dimensional image data sets is carried out with the usual reconstruction methods for different time steps during the spreading of the contrast medium. Then, by subtraction of a mask image data set, information about the spreading of the contrast medium may also be included. However, this procedure is extremely time-consuming and also time-critical since the rotations take up a longer period of time, during which a change in the contrast medium situation takes place.